Unease over austerity has flared in Britain's Conservative government, with a prominent minister resigning to protest what he described as indefensible cuts in benefits for the disabled.

Iain Duncan Smith quit Friday, two days after the government unveiled a budget that cut disabled benefits even as it offered tax relief to the better-off. In his resignation letter, the work and pensions secretary says he believed the changes were "a compromise too far."

Duncan Smith says he couldn't accept policies driven by politics rather than economics — and that the austerity principle of "we are all in this together," had been abandoned.

Duncan Smith is also campaigning for Britain to leave the European Union, a move Cameron opposes.

Cameron says he was surprised and puzzled by Duncan Smith's decision.